The effect of two pesticides, the diflubenzuron (DFB) and the Flucycloxuron (FCX) has been studied on a cellular model: Paramecium sp., a ciliated protiste. The treatment with the DFB in the concentrations of 10 and 20 microg/ml reduces the growth of this protiste appreciably. The survey of the respiratory metabolism by the polarography technique (Oxygen electrode) shows a sensitive inhibition of the oxygen consumption by the studied protiste. In the case of the FCX, the treatment with the two concentrations (10 and 20 microg/ml) reveals an inhibition of the ciliated protiste growth; however, this pesticide inhibits the respiratory metabolism of ciliated protiste. This effect is a lot more marked with the FCX that with the DFB. The coloration with neutral red showed a perturbation in cuticle level, translated by the penetration quantity of the color in treated cells, especially at 20 microg/ml of FCX.